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Sahara stirling

 Just put the cold part under the earth, the hot part in the sun
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Create a low temperature stirling engine [see link]; put the hot end in the baking Sahara sun, while you bury the cool end deep in the ground; the temperature difference will be high enough. At night, the process reverses as the Sahara can become very cold, while the ground retains heat.

No need for solar dishes, precision mirrors or solar towers. This should be simple and cheap!

—django, Dec 20 2005

Low temperature stirling engine http://www.bsrsolar.com/core1-1.php3
Low temperature stirling pot [django, Dec 20 2005]

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       Great idea. what is the theoretical energy per unit area you could extract from this? I'm geussing it's fairly low compared to solar cells, but much cheaper to set up.
—xaviergisz, Dec 20 2005
   

       But this would last a lot longer in the Sahara, what with the wind and sand scratching solar panels and all.
—DesertFox, Dec 20 2005
   

       As opposed to lots of moving parts? Which can be covered, yes, but sand gets everywhere...
That being said, bun.
—moomintroll, Dec 20 2005
   

       I like the idea,   

       Might i propose an additional source of coolant:   

       -55 Celsius air sucked down from the lower stratosphere through a cooling chimney (the chimney wouldn't necessarely have to reach all the 10 km to the stratosphere, a small diameter hose suspended from stratospheric balloons goes a long way) , using a relative small percentage of the generated power from the stirling engine (as the temperature difference is likely larger than an underground passive adiabative expansion network).   

       Stretch this concept the extra "mile" and put an australian solar tower as "hot chimney" next to the "Cold chimney" , connect the two and replace the windturbines with some kind of internal piston or use linear magnetic induction for power generation instead. naturally the proposed solar tower would also be an inflatable structure.   

       How about stretching the concept some more miles and have stirling engines on the moonsurface, where is even a larger temperaturedifference between anything exposed to sun with objects hidden undergound or in the shadow inside a mooncrater, where a nice working fluid (read ice -> steam) is likely to be obtained.
—jvanguts, Dec 20 2005
   

       I wanted to add that you could use a very cheap heat storage device (a thermal battery of sorts). Just next to the kettle, you bury a reservoir of oil in the ground, which you attach with a pipe to the hot part of the kettle; during the day, you siphon off some of the hot air from the stirling-kettle, with which you heat up the oil; at dusk, when the desert quickly starts to cool and our stirling-process reverses, you release the heated oil and let it flow to a reservoir under the cold part (which now, at night, functions as the hot part); during the night, the oil gives off its heat, making the stirling more efficient still. Come dawn, the process switches again, and you use a very small part of the stirling power to pump up the oil to its original reservoir.
—django, Dec 21 2005
   

       One nice extra: the desert has lots of sand nearby; perfect to make glass; so why don't we make the hot part of the stirling kettle from a big glass "lid"; no need for precision work as with mirrors for disch-stirlings; just make a big strong glass bowl-lid and put it over your stirling kettle; the weight of the lid alone should withstand the rather low operating pressure of our low-temperature stirling kettle.   

       Maybe glass is cheaper than iron or steel or aluminum lids.
—django, Dec 21 2005
   

       //55 Celsius air sucked down from the lower stratosphere through a cooling chimney (the chimney wouldn't necessarely have to reach all the 10 km to the stratosphere, a small diameter hose suspended from stratospheric balloons goes a long way)//   

       You obviously saw "The Day After Tomorrow" and slept through science class when they went over PV = nRT.   

       The -55 degree air is cold because it is less dense. In bringing it down to ground level, it will heat up.
—Madai, Dec 21 2005
   


 

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